5) What are (or can be) the main differences between oils of the same type, i.e. what's the difference between a 'good' and a 'bad' oil?
It all comes down to honesty really.....so beware! A good oil is what it claims to be on the can. 10W/40? Does it really pass the cold test at -25C? Quite a few I've tested do not. There is usually an API spec quoted, such as API SH or SL. These are car-based, and a good basic quality guide. If absent, leave it on the shelf, and avoid lawyer-speak:
'meets the requirements of....' or 'recommended (by whom?) for use in....'.
Then there is the 'synthetic' minefield! Provided the price hasn't been pushed up by shipping an average oil 5000miles from the West coast of the USA, you get what you pay for. The best performance oils are made in the more developed European countries, but low price buys the cheap 'modified mineral' synthetic and not much of it, with a poor multigrade polymer. As is so often the case, quality follows cost.
6) What are the likely consequences of using poor-quality oil?
Usually, these are fairly long term, except in racing. Think of the oil as a liquid component, and poor oil as a cheap pattern spare. In a road car long-term reliability and performance retention (i.e. acceleration figures below new spec., fuel and oil consumption above) are the casualties. Particularly in a high performance or racing car,
the effects can be more immediate and catastrophic.
7) Some oil companies have run advertising campaigns that imply their products have special, unique qualities. Can these adverts be taken seriously?
Yes and no! Generally adverts in magazines are honest, with marketing-speak terms such as ‘Magnatec’ and ‘Electrosyntec’ really being code words for esters, which are particularly beneficial in performance engine oils. No manufacturer has any unique ‘secret’, so it’s all down to providing the best possible blend for the job at the right price, and making it clear that you get what you pay for. I personally think that the importance of shear stability or ‘stay in grade’ is not stressed enough when quality is talked about.
What is dodgy though is claiming that a mineral based oil with a few percent of modified mineral (‘hydrocracked’) synthetic is the DB’s and suitable for racing, etc. when it clearly isn’t.
Also, there is endless semantic manoeuvring and lawyer-speak around The Magic Word ’synthetic’.
For instance, a ‘synthetic’ oil is invariably semi-synthetic (’Ah! We didn’t say it was all synthetic did we?), and, if low priced, invariably the modified mineral type synthetic. It is a sad fact that you get what you pay for, but even so, stick to the reputable UK/European brands, and remember that shipping an oil half way around the world doesn’t automatically make it better than one made in your home town.
As for TV advertising…well, does anybody believe it? Due to its huge cost, a TV advertising campaign can significantly raise the cost of specialist items such as oil. Everybody assumes it’s just a few pence per gallon, but it can be pounds per gallon.)
Please can you explain the grading system? What is meant by the weight of an oil? What does 10W/40 mean for example?
Weight means viscosity, or resistance to flow. Water and paraffin flow very easily, so they are low or light viscosity. Golden syrup or 140 gear oil do not come out of the can so easily, so they are high or heavy viscosity.
Especially with oils, temperature is very, very important. An oil which looks ‘heavy’ at 20C will be very ‘light’ at 100C. People sometimes say, ‘I drained the oil when the engine was hot and it ran out like water…’ so I say, ‘Good! It’s supposed to be like that!’
The American Society of Automotive Engineers (SAE) ratings cover cold starts and ‘up and running’ viscosities. There are two sets of standards, the ‘Winter’ (W) ratings, and the 100C standard ratings. (‘W’ does not, repeat not, mean ‘weight’!)
So a 10W/40 oil has to pass a 10W cold viscosity test at -25C, and a SAE 40 test at 100C. In an oil lab there will be a refrigerated viscosity measuring device for the ‘W’ tests and another at 100C for the standard SAE tests. There are 6 ‘W’ ratings from the difficult 0W at -35C to the dead easy 25W at -10C, occasionally used in India for example!
The whole point of these Winter ratings is to assist cold starts, to get the oil circulating quickly, and to avoid power and fuel wasting drag as the engine warms up. Once it is warmed up, the 100C ratings count. There are 5 of these, 20, 30, 40, 50, and 60 although why anybody bothers with 60 in the 21st Century is a mystery to me!
Sorry folks, but I’ve got to get technical. Viscosity is measured in standard units called ‘Centistokes’, names after a Victorian engineer, Sir George Stokes, who used to time ball bearings as they sank through oil. SAE 30 for example is from 9.3 to 12.5 Centistokes, and SAE 40 follows on at 12.5 to 16.3, although most SAE 40 oils are in the middle at about 14.
Now this is something most don’t realise: engines do not know what grade of oil they’re running on. They’re not clever enough! So an engine filled with 10W/40 will be running on a viscosity of 14 at 100C, but with a sump temperature of 90C its seeing a viscosity of 18, so as far as the engine is concerned it’s running on SAE 50. Likewise, at 110C, it’s down to 11 Centistokes so it ‘thinks’ it’s on a SAE 30! (Which is preferable.)
The lesson is, do not use power and fuel-wasting thick oils in cool climates. A decent 10W/40 or even thinner is perfectly OK unless you’re running a classic with wide clearances and a slow oil pump.
Radical race cars use 1300 Suzuki Hyabusas and work them very hard. (Didn’t one take the old Nurburgring absolute record at one point?). They use our high-ester 15W/50, but that’s OK because they see oil temps around 130C! (No problem for the oil or the engine, but they do fit special oil seals.) At 130C the true viscosity is 10cSt, so the engine thinks its on a thin SAE 30, which keeps it happy.
8) What is the best type of oil to use in a road car for general use? Is fully synthetic a waste of money?
Personally I’d go for a shear-stable part ester synthetic, SAE 10W/40 or 5W/40. The ‘shear-stable’ bit (ie, a decent quality multigrade polymer) is actually more important than the ‘synthetic’ part!
If strapped, I’d go for a shear-stable mineral based oil rather than a ‘synthetic’ of dubious stability that’s probably based on modified mineral oil anyway. Unless you’re covering a huge annual mileage, genuine 100% synthetics are probably an extravagance. High mileage long-distance fans can use a light full synthetic and save on fuel and oil changes, and cut overhaul costs if things get to that stage, but more later…..
9) What are the main differences between 2 and 4-stroke oil? Why does 2-stroke oil have to be mixed with fuel?
2-stroke oil has a very short working life, straight in and out, and it gets burnt. The 2-stroke engine doesn’t have a sump full of oil and the bearings are all rollers, so there’s hardly any oil drag, hence no need for multigrades. Long term stability is obviously not a problem!
But, 2-stroke must burn off without leaving any plug-fouling or detonation-initiating deposits. The detergent and anti-wear additives used in 4-stroke oil leave hard white ash behind when they burn, just what you do not need in a 2-stroke. So 2-stroke oils use low-ash detergents and dispersants, and the better types use ester synthetics to act as anti-wear compounds.
With current environmental concerns, smoke is a sensitive issue, so most ‘road’ 2-stroke oils are now low smoke, which requires yet another type of synthetic base designed to burn off invisibly. For some rather basic but very high-revving air-cooled racing 2-strokes there’s still some sense in using blends with that marvellous anti-seize liquid, castor oil!
Due to crankcase induction and compression, the classical 2-stroke obviously cannot have an oil-filled sump, so the only way to keep an oil film on anything was to add oil to the fuel, or inject oil into the crankcase space where it could mix with the fuel vapour. There are now some engines where the fuel and oil are injected separately, but the oil is still burnt.
10) How important is it to change oil regularly? What are the implications of failing to do so?
It is only really important to change oil regularly if the engine covers a low annual mileage made up of slow, short runs. This is being cruel to the oil and the engine! The oil, regardless of its quality, gets full of fuel and water vapour, and never gets the chance to evaporate it all off with a long fast run. The consequences are corrosion, ring and bore wear. It is essential to do a change at least once a year, even if the recommended mileage hasn’t been covered. On the other hand, if you eat up the miles on long blasts the engine and its oil will love it, so with a top-quality oil it is OK to cheat a little on oil drain periods.
continues............................
